1. Field of the Invention
The present invention relates generally to electronic devices, and more particularly to an electronic device having a heating component that generates heat and a heated component that needs to be heated provided together in the same case.
2. Description of the Related Art
In general, electronic devices have various heating components as represented by semiconductor devices on a board provided inside a case. If the temperature of a heating component is not maintained at a predetermined operating environment temperature, other electronic components mounted on the board may be damaged or the heating component (such as a semiconductor device) itself may be prevented from operating properly by heat.
Therefore, in an electronic device having a heating component, a heat dissipation part that dissipates heat generated in the heating component is provided as described in Japanese Laid-Open Patent Application No. 2005-159560 or the heating component is cooled with a Peltier element as described in Japanese Laid-Open Patent Application No. 11-026852. Further, the electronic device is configured to discharge the heat radiated from the heating component outside the case with efficiency.
Optical fiber amplifiers (hereinafter referred to as “optical amplifiers”) are known as electronic devices. Some optical amplifiers employ an optical fiber doped with a rare-earth element for long-range light signal communications. Of these, erbium-doped fiber amplifiers (EDFAs) are well known.
The erbium-doped optical fiber (EDF) has a disposition to amplify a light signal having a wavelength in the 1.5 μm wavelength range with light having a wavelength in the 0.98 μm or 1.48 μm range (referred to as “pump light”). By inputting the light signal and the pump light to the erbium-doped optical fiber, the signal light is amplified and output. The characteristics of the erbium-doped optical fiber depend on the length, the dopant and doping density, the pump light wavelength, the pump light power, the temperature, etc., of the erbium-doped optical fiber.
In practical use, an erbium-doped optical fiber having a length corresponding to a dopant and doping density is provided in an optical amplifier so as to achieve desired amplification characteristics, and a laser used for pump light also is controlled to be constant in wavelength and output. However, with respect to temperature, the dependence on use environment temperature causes amplification characteristics to vary depending on the use environment temperature. Therefore, it is necessary to keep amplification characteristics constant by keeping constant the temperature of the erbium-doped optical fiber.
It is known to keep constant the temperature of the erbium-doped optical fiber by keeping it constant at the upper limit of the use environment temperature with a heater. In order to keep the erbium-doped optical fiber at a constant temperature, the erbium-doped optical fiber is wound around inside a metal having good heat transfer characteristics, and a heater is attached to the metal to increase the temperature. Further, it is necessary to cover the metal with a heat insulator or provide the metal in a closed space where a sufficient heat insulation distance is ensured in order to prevent heat from escaping around or prevent the temperature from varying.
FIG. 1 is a schematic diagram showing a conventional optical amplifier 1 to which an erbium-doped optical fiber is applied. The optical amplifier 1 includes a first board 2 and a second board 16 in a case 15. A laser diode (LD) 3, an LD drive unit 4, and an LD temperature controller 8 are provided on the first board 2. Further, an optical amplification element 17, a heater drive unit 20, and a heater temperature controller 22 are provided on the second board 16.
The LD 3 generates pump light for an amplifying operation. Normally, the required output power of the LD 3 is several tens to several hundreds of mW. It is desirable to dissipate heat generated in the LD 3 with efficiency in order to obtain this output stably. Therefore, radiating (heat dissipating) fins 14 are thermally coupled to the LD 3, so that the heat is directly dissipated through these radiating fins 14.
Further, the optical amplifier 1 shown in FIG. 1 has a Peltier element 9 provided on the LD 3 so as to forcibly cool the LD 3 with the Peltier element 9 in order to further improve its heat dissipation characteristics. The heat generated in the Peltier element 9 by the cooling of the LD 3 is dissipated outside using the radiating fins 14.
On the other hand, the optical amplification element 17 provided on the second board 16 has an erbium-doped optical fiber wound around an EDF reel 19. In this case, it is desirable to wind the erbium-doped optical fiber with a radius of, for example, 20 mm or more in view of its bending loss characteristics, and it is desirable to contain the optical fiber for a length of, for example, several tens of meters or more because of gain. Therefore, the range that requires increases in temperature widens. Further, in the case of a use environment temperature range of 0° C. to 65° C., it is necessary to increase temperature from 0° C. to 65° C. if the environmental temperature is 0° C.
Therefore, a heater 18 is provided in the optical amplification element 17, so that the optical amplification element 17 is heated to the use environment temperature with this heater 18. Further, the optical amplification element 17 is housed inside a heat insulator 24 so as to prevent the applied heat from escaping outside.
FIG. 2A is a block diagram showing a system for controlling the temperature of the LD 3. FIG. 2B is a block diagram showing a system for controlling the temperature of the heater 18. As shown in FIG. 2A, the LD 3 is driven by an LD oscillation control circuit 5 and an LD driver circuit 6 forming the LD drive unit 4 (FIG. 1). Further, the driving increases the temperature of the LD 3, which is detected by an LD temperature sensor 11 provided near the LD 3 as shown in FIG. 1.
The temperature detected by the LD temperature sensor 11 is fed to an LD temperature monitoring circuit 12 forming the LD temperature controller 8 (FIG. 1), and the LD temperature controller 8 determines based on this fed temperature whether it is necessary to drive the Peltier element 9. If the LD temperature controller 8 determines that the radiating fins 14 alone do not dissipate heat sufficiently, the LD temperature controller 8 drives the Peltier element 9 through a device driver circuit 10 to forcibly cool the LD 3. The starting and stopping of this driving of the Peltier element 9 is suitably performed in accordance with the temperature of the LD 3 fed from the LD temperature sensor 11.
Further, as shown in FIG. 2B, the temperature of the heater 18 is controlled based on a signal fed from a heater temperature sensor 21 (also shown in FIG. 1) that measures the temperature of the EDF reel 19 (around which the erbium-doped optical fiber is wound) provided inside the optical amplification element 17. A heater temperature monitoring circuit 23 forming the heater temperature controller 22 controls the heater drive unit 20 based on the temperature of the EDF reel 19 transmitted from the heater temperature sensor 21, so that the temperature of the EDF reel 19 is controlled to the above-described predetermined environmental temperature.
As shown in FIG. 1, the optical amplification element 17 having the erbium-doped optical fiber serving as an amplification medium provided therein and the LD 3 serving as a pump light source are often housed inside the single (same) case 15 as the optical amplifier 1. Therefore, the optical amplification element 17 (erbium-doped optical fiber) desired to be kept at high temperature and the LD 3 desired to be cooled or have its heat dissipated are provided close to each other.
Conventionally, the heat transfer channel for the heat generated from the LD 3 and the heat transfer channel for the heat fed to the optical amplification element 17 are separated and cut off from each other. That is, in the LD 3, the heat generated therein and the heat discharged from the Peltier element 9 are guided to the radiating fins 14 so as to be discharged outside the case 15 from the radiating fins 14. Therefore, the radiating fins 14 are often provided external to the case 15.
On the other hand, the optical amplification element 17 is housed inside the heat insulator 24 to thermally separate the inside of the LD drive unit 4 and the optical amplifier 17 so that the heat generated by the heater 18 is prevented from being dissipated outside the case 15.
Thus, according to the conventional optical amplifier 1, since it is necessary to mount components having conflicting thermal channels of heat dissipation and heat application, electric power is consumed to control their respective temperatures. Therefore, there is a problem in that the difference between the temperature of the optical amplification element 17 and the ambient temperature grows to increase the electric power for heating particularly at a low-temperature time.